When should I retopologize?
You should start with the face , add a plane rotated on you  left to right axis and then add a shrink-wrap modifier and also enable face snapping this will try their best in keeping your extrusions with the sculpted topology , keep the plane on the noseBridge and also add a mirror , then start extruding the side till the eyes and then take your extrusion around the eyes , like this you can cover the whole body properly , and try yr best keeping them quads.
You can go around in this fasion